1. Field of the Invention
The present invention relates to the general field of devices and methods making it possible to separate, or filter a flow of gas conveying liquid or solid particles, such as oil, from a flow containing a gas/particles mixture. A special field of application of the invention is that of gas turbine (turbojet and turboprop engines) aircraft engines.
2. Description of the Related Art
Gas turbine aircraft engines comprise enclosures containing bearings and gears which are lubricated and cooled with oil. In order to prevent oil from leaking out of the enclosures, seals are positioned between the rotating parts and the stationary parts of the enclosures, or even between the rotating parts. Among the various seals available, those having the longest service life are labyrinth seals and brush seals, with no contact between the parts in the first case and a very limited contact in the second case.
To provide perfect sealing of the enclosures provided with labyrinth seals and brush seals, air flow has to go through the seals, with such air flow being generally sampled at one stage of the engine compressor. Using such a method also implies the provision of devices separating oil from air to be exhausted outside the engine. Such devices—commonly referred to as oil separators—are well known per se. Reference can be made, for example, to documents EP 1582703, U.S. Pat. Nos. 4,981,502 and 6,033,450 which disclose various types of de centrifugal oil separators.
To operate properly, the oil separators of the centrifugal type must rotate at high speed, whereas the flow of air and oil circulates and is filtered through foams. The higher the rotating speed of such oil separators, the higher the pressure drops generated. As the enclosure seals are so designed as to be operated with a predefined pressure difference, when the oil separator generates a higher pressure drop, the sampling pressure at the compressors must be increased. Such sampling at a higher pressure is harmful to the engine performance, since the air sampled for operating the oil separators does not participate in the propulsion of the turbine engine, but also for cooling the bearings and the gears, since sampling at a higher pressure implies air being sampled at a higher temperature. Besides, the air flow which is taken from a stage of the compressor depends on the engine operation speed, so that the minimum air flow required for sealing the enclosures and the operation of the oil separators are calculated on the basis of the slow phase of the engine (such phase corresponds to the engine operating speed, during which the sampled air flow is the lowest). During the other operating phases of the engine, and more particularly at full speed, the flow of air going through the enclosures is in excess as compared to what is sufficient to provide the sealing of the enclosures, which causes an over-consumption of oil with all the harmful effects entailed therein (pollution, additional cost, etc . . . ).
Besides, the centrifugal oil separators currently used are subjected to a very specific and restrictive integration in the turbine engine, because of the existing rotating parts which have to be driven within the oil separators.